LONDON (REUTERS) - A Roman Catholic cardinal who resigned as head of the church in Scotland apologised on Sunday for sexual conduct which he said had "fallen below the standards expected of me".

Cardinal Keith O'Brien, who was Britain's most senior Catholic cleric, resigned on Feb. 25 as archbishop and said he would not take part in the conclave to elect a new pope after newspaper allegations of inappropriate behaviour with priests.

"I wish to take this opportunity to admit that there have been times that my sexual conduct has fallen below the standards expected of me as a priest, archbishop and cardinal," he said in a statement posted on the Scottish Catholic media office website on Sunday.

"To those I have offended, I apologise and ask forgiveness. To the Catholic Church and people of Scotland, I also apologise.

"I will now spend the rest of my life in retirement. I will play no further part in the public life of the Catholic Church in Scotland."

O'Brien's resignation as archbishop of St. Andrews and Edinburgh was announced a day after the Observer newspaper reported that three priests and one former priest from a Scottish diocese had complained over incidents dating back to the 1980s.

The Observer said O'Brien, an outspoken opponent of moves in Britain to legalise gay marriage, had been reported to the Vatican over the unspecified incidents.

The cardinal initially rejected the allegations and said he was seeking legal advice. He said he would not take part in the conclave to avoid focusing media attention on himself.

Last year, O'Brien's comments labelling gay marriage "a grotesque subversion" landed him with a "Bigot of the Year"award from gay rights group Stonewall.